Patent GB-1010313-A (GB)
Title: A system for setting orthogonal equalizers for the equalization of attenuation and transit time
IPC: H04J1/08
Filed: 1963-05-22
Abstract: 1,010,313. Equalization systems. TELEFUNKEN PATENTVERWERTUNGSGESELLSCHAFT. May 22, 1963 [May 24, 1962], No. 20384/63. Heading H4R. In a method of setting orthogonal equalizers, particularly cosine equalizers, in a multi-channel carrier frequency transmission system, a number of pilot voltages are transmitted, distributed over the frequency range of the transmission system, and fed at the receiving side via filters, to isolate each of the pilot frequencies, to a switch by which the individual pilot frequencies are connected in periodic succession, from the lowest to the highest frequency and vice versa, to an amplifier and a rectifier so that the attenuation frequency characteristic of the transmission system including the equalizers is converted to a voltage variation periodic in time which has frequency components which correspond to a series of orthogonal functions, e.g. a cosine series, which may be used to control the setting of the equalizers and in which the equalizers are controlled in a stepwise manner by a pulse generator, a check being automatically made after the first step to ensure that the step has led to a reduction in distortion, the direction of stepping being reversed if it has not, the control steps being continued until a minimum distortion is produced when the control is switched to the succeeding equalizer. In the embodiment shown in the Figure, seven pilot frequencies distributed substantially equally over the whole transmission band to be equalized are fed from generators G 1  to G, and are applied to the line L via a coupling member EK and a transmitting amplifier SV 1 . At the receiver the signals are passed through cosine equalizer members C 1  to C 6  provided with amplifiers SV 2  and SV 3  to compensate for the fundamental attenuation. The received pilot voltages are fed to pilot filters PF 1  to PF 7  through a decoupling member AK and the outputs of the filters connected to a mechanical or electronic switch S 1  which connects the pilot frequency voltages cyclically to an amplifier HV and rectifier HG. The resulting signal, the waveform of which is an analogue of the amplitude-frequency characteristic of the line and equalizers, is fed to the inputs of filters F 1  to F 6  which filter out the first six components of the frequency spectrum of the voltage waveform, the magnitude of these components indicating the degree of adjustment required of the respective cosine equalizers. The method of adjustment of the equalizers is as follows, the control sequence is initiated by a pulse at e which changes bi-stable circuit B 1  into its operating condition and opens gate t I  to allow pulses from oscillator A to pass to the gate t III . Ring switch R with switch levels S 2  and S 3  is initially in its preferred position 1 which connects the output of filter F 1  to the amplifier NV over switch S 2 , and the output of gate t III  to terminal e 1  and hence to the setting device E 1  of cosine equalizer member C 1 . The output of filter F 1  after amplification in NV and rectification in NG is applied to a Schmitt trigger T 1 , if the output exceeds the acceptable minimum, trigger T 1  closes gate t II  and opens gate t III  and a pulse passes from pulse generator A to the setting device E 1  to step the setting device by a setting increment. If the step results in an increase in the output of filter F 1 , corresponding to an adjustment step in the wrong direction, the positive going edge, differentiated by D, operates trigger T 2  and changes the state of bi-stable circuit B 2  which varies the bias on setting devices E 1  to E 6  and ensures that the next pulse received from the generator A results in an adjustment step in the correct direction. A reduction in the output of filter F 1  does not operate trigger T 2  and the bias on the setting devices E 1  to E 6  is left so that further pulses will operate the devices in the correct sense. When the output of filter F 1  is reduced to the acceptable level, trigger T 1  reverts to its unoperated condition, closes gate t III , to prevent any further pulses being fed to the setting devices E 1  to E 6 , and opens gate t II  so that the next pulse from the generator A is fed to ring switch R and steps the switch to the position for checking and adjusting the equalizer C 2  via filter F 1  and setting device E 2 . The sequence is repeated until all the equalizers are adjusted, when the final pulse to revert the ring switch R to its initial condition feeds a pulse from R to reset the bi-stable device B 1  to its initial condition to await a subsequent pulse at e to initiate a subsequent equalizing operation. The adjustment of the equalizer network may be by the variation of current through a thermistor in the network. If the time of operation of the ring switch is longer than the pulse period of the generator A, a delay circuit V and a further gate t v  may be included, as shown dotted, to interrupt the pulse train until the ring switch R has operated and the system is ready to accept further setting pulses. Specification 801,120 is referred to.